Thursday, November 10, 2005

Did volcano cause a sea level rebound?

05 November 2005

From New Scientist Print Edition.

WE CAN put away the life rafts for now. The near doubling in the rate of sea level rise during the 1990s was probably due in part to the delayed effects of the eruption of Mount Pinatubo in the Philippines - and not runaway melting of ice caps.

Volcanic eruptions have long been known to cause a global chill by filling the upper atmosphere with particles that block out some of the sun's radiation. Pinatubo's 1991 blast cooled the atmosphere for two years, but no one was sure whether similar cooling occurred in the oceans.

Now John Church of the CSIRO in Australia has combined observations of the oceans' heat content with climate simulations to calculate that ocean surface temperatures fell by up to 0.5 °C in the months after the eruption in 1991 (Nature, vol 438, p 74). Since cooling reduces the water's volume, he calculates that Pinatubo should have taken 5 millimetres off sea levels worldwide during this period.

Since then, the oceans have been regaining heat, but this warming happens more slowly that it does in the atmosphere. Church calculates that the Pinatubo rebound explains half of the surge in sea level rise measured by satellites between 1993 and 2000. During that period, sea levels rose by 3.2 millimetres a year, compared with an average of 1.8 millimetres since 1950.

We hear much about whether science has "proven" something to be true or not. Science cannot deductively prove anything to be true. It can only deductively prove something to be false and inductively demonstrate the likelihood that something is true. This is because we will never know everything. Haven't we been told that the oceans are rising because the polar icecaps are melting because of global warming? Apparently it wasn't true. It's been touted as though it were true, but mere assertions are not the stuff of "proof". Keep this in mind when you hear reports from junk science like evolution and global warming.